In a mine, there is typically a volume of material having a higher concentration (ore grade) of the desired mineral, than the surrounding material. The material with higher grade mineral is generally termed the “ore body”, and the material around the ore body is generally termed “host material”.
Underground mining operations are designed to extract as much of the ore body, and as little as possible of the host material. One of the effects of inefficient mining is dilution, whereby the mixing of host material together with ore from the ore body reduces the overall ore grade.
Dilution has a significant detrimental effect on the economics of a mining operation. If the mining operation extracts and processes a tonne of host material the costs involved are the same as for targeted ore, however the mine does not receive the revenue that would have been in extracted material. Therefore profits are reduced by the value of the ore that was expected, but not received. While underground cave-type mines (Sublevel Caves and Block Caves) typically involve a low cost per tonne of material extracted; they suffer from high rates of dilution.
In the mining arts problems of dilution have been investigated and addressed by the use of various marker devices. The markers are typically used to measure ore flow in mass mines. These flow measurements are often performed with metallic markers having identification codes inscribed thereon. Being metallic, these markers may be conveniently retrieved by magnetic separation means already existing in the mining process.
More recently, radio frequency identification (RFID) technologies have been used to uniquely identify markers. Such markers may be read by one or more detector devices disposed about the mine.
Typically, ore movement measurements commence with the installation of a series of markers into various positions of the mine, or into mined material. The identification codes and installation locations are recorded. At one or more points in the extraction process, the markers are retrieved (or read in the case of RFID markers) and the codes recorded along with other data such as time of retrieval.
The installation position and retrieval details of a set of markers provide valuable ore flow information to mine management. By knowing the original installation position of each marker, along with the time and location of extraction, the movement of rock in an underground ore body can be analysed, revealing flow over time.
The measurement of ore movement is often required in open-pit mining. With open pit mining, the miner has the opportunity to choose where to send extracted material. Material believed to be ore is sent to the mill; whereas material believed to be waste is sent to a waste heap. The ore is usually sampled before blasting, and the boundary between targeted ore and waste is mapped. However, the process of blasting moves the material, and the ore-to-waste boundary moves. It is desirable for mining management to measurement ore movement, to reduce lost ore and the processing of ore diluted by waste.
Ore movement measurements are labour intensive because mine staff must manually recover the markers. Prior art techniques also lack precision and resolution.
A problem with these techniques using markers is that the collection of data occurs at the time the ore is extracted. This can lead to misinformation, or information that is provided when it is too late to make any adjustments to the mining process.
Measurement of rock movements is required in other contexts, such as in underground cave-type mines. It is often important to measure the upward propagation of the cave as it develops. As ore is being extracted from deep under the ground, the material above the extraction needs to “cave” and fall in to replace the extracted material. With “block cave” mining, the cave gradually propagates upwards to the surface, and eventually a crater forms on the surface. If, for whatever reason, the cave stops propagating, a cavity will form between the ore that has broken and fallen and the ore that is still in place. If the mining operation continues, this cavity will gradually grow in size as material is extracted from below. Eventually, the ceiling of this cavity will collapse. If the cavity was large before the collapse, an “air rush” can occur, because the highly pressurised air must escape through some means. If the air finds its way into a mine drive, it can have fatal consequences. The effect is similar to a blast. It is therefore important to measure the cave's propagation.
Current technology to measure cave propagation involves “time domain reflectometry” (TDR). Typically, holes are drilled from either the surface or from a tunnel through the ore body. These holes are populated with cables and associated electronic equipment, and a signal is transmitted along the cables. The signal reflects off the terminus of the cable, with the length of time taken for the signal to travel from the source to the terminus of the cable and back to a detector is measured. As the cave propagates, the end of the cable breaks off and therefore becomes shorter, thereby resulting in a shorter reflection time. A common problem with this approach is seen where the ground above the cave-front splits and, the two parts move relative to each other. This movement often cuts the cable at points higher than the cave front, resulting in incorrect data being provided.
It is an aspect of the present invention to overcome a problem of the prior art by providing improved methods, systems and markers for use in mining. It is a further aspect of the present invention to provide an alternative to the methods, systems and markers of the prior art.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.